Jung-Yao Chen

Nonvolatile Perovskite‐Based Photomemory with a Multilevel Memory Behavior

Solution-processable organic-inorganic hybrid perovskite materials with a wealth of exotic semiconducting properties have appeared as the promising front-runners for next-generation electronic devices. Further, regarding its well photoresponsibility, various perovskite-based photosensing devices are prosperously developed in recent years. However, most exploited devices to date only transiently transduce the optical signals into electrical circuits while under illumination, which necessitates using additional converters to further store the output signals for recording the occurrence of light stimulation. Herein, a nonvolatile perovskite-based floating-gate photomemory with a multilevel memory behavior is demonstrated, for which a floating gate comprising a polymer matrix impregnated with perovskite nanoparticles is employed. Owing to the well photoresponsibility introduced by the embedded nanoparticles, the device is enabled to access multiple wavelength response and the functionalities of recording power/time-dependent illumination under no vertical electrical field. Intriguingly, a nonvolatility of photorecording exceeding three months with a high On/Off current ratio over 104 can be achieved.

New poly(selenophene–thiophene) bearing π-conjugating spacers for polymer field-effect transistors and photovoltaic cells

Five new poly(selenophene–thiophene) polymers, including PSe4TV, PSe4TT, PSe4T2T, PSe4TTT, and P2Se4TTT, were synthesized via Stille coupling polymerization and used various π-conjugated spacers of vinylene (V), thiophene (T), bithiophene (2T), and thieno[3,2-b]thiophene (TT). Tuneable structural, optical, and electrochemical properties of polymers were observed because different π-conjugated building blocks in the main polymer chain affected the conformation of the polymer backbone. Details of polymer morphologies were systematically investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXD). P2Se4TTT possessed the smallest energy band gap, densest molecular packing structure as well as fibrillar-like nanostructures among the studied polymers because the TT moiety could enhance the coplanarity of the polymer backbone and the inserted biselenophene reduced the hindrance of thiophene side chains. Hence, the highest field-effect mobility of this set of polymers was determined to be 0.27 cm2 V−1 s−1 from a P2Se4TTT-based field-effect transistor device with a high on/off ratio over 105. The power conversion efficiencies (PCEs) of the photovoltaic cells based on polymer/PCBM blends were in the range of 0.43%–1.18% for our synthesized polymers. Among them, the P2Se4TTT-based device could achieve the best PCE of 2.29% using a o-dichlorobenzene–1,8-diiodooctane (98:2 v/v) mixture as the processing solvent. The enhancement of active layer uniformity responded to the increment of efficiency. The abovementioned results demonstrated that the newly designed polymers could serve as promising candidates for optoelectronic device applications of polymers.

Uniform Luminous Perovskite Nanofibers with Color‐Tunability and Improved Stability Prepared by One‐Step Core/Shell Electrospinning

A one-step core/shell electrospinning technique is exploited to fabricate uniform luminous perovskite-based nanofibers, wherein the perovskite and the polymer are respectively employed in the core and the outer shell. Such a coaxial electrospinning technique enables the in situ formation of perovskite nanocrystals, exempting the needs of presynthesis of perovskite quantum dots or post-treatments. It is demonstrated that not only the luminous electrospun nanofibers can possess color-tunability by simply tuning the perovskite composition, but also the grain size of the formed perovskite nanocrystals is largely affected by the perovskite precursor stoichiometry and the polymer solution concentration. Consequently, the optimized perovskite electrospun nanofiber yields a high photoluminescence quantum yield of 30.9%, significantly surpassing the value of its thin-film counterpart. Moreover, owing to the hydrophobic characteristic of shell polymer, the prepared perovskite nanofiber is endowed with a high resistance to air and water. Its photoluminescence intensity remains constant while stored under ambient environment with a relative humidity of 85% over a month and retains intensity higher than 50% of its initial intensity while immersed in water for 48 h. More intriguingly, a white light-emitting perovskite-based nanofiber is successfully fabricated by pairing the orange light-emitting compositional perovskite with a blue light-emitting conjugated polymer.

A stable, efficient textile-based flexible perovskite solar cell with improved washable and deployable capabilities for wearable device applications

Organic–inorganic hybrid perovskite solar cells (PVSC) have appeared as promising high power-per-weight power systems for wearable electronic devices. Herein, we utilized a low-temperature electrodeposited tin oxide (SnO2) electron-transporting layer (ETL) coupled with a thin PCBM ETL and a functional encapsulating layer to realize an efficient, stable textile-based flexible PVSC. We first demonstrated that an easily accessible elastomer can serve as an effective encapsulating material for the fabricated flexible PVSC, as exemplified by the largely improved ambient stability and waterproof properties. Furthermore, we established that the good adhesive properties generated by the elastomer can largely enrich the deployable capability of the completed device stack as evidenced by the effortless integration of a completed device stack onto a textile. As a result, a ∼15% textile-based flexible PVSC with improved ambient stability and washable capability was demonstrated. A proof-of-concept device was successfully integrated with other electronic devices on a unitary textile to serve as an efficient power supply system for wearable electronic devices. The findings revealed in this work can promote the future potential applications of PVSCs in wearable device applications.

Unraveling the stress effects on the optical properties of stretchable rod-coil polyfluorene-poly(n-butyl acrylate) block copolymer thin films

We report the synthesis, morphology, and photophysical properties of new conjugated rod-coil block copolymers consisting of poly[2,7-(9,9-dihexylfluorene)] (PF) conjugated rods and soft poly(n-butyl acrylate) (PBA) coils for stretchable light-emitting device applications. The PF-b-PBA thin films could form obvious self-assembled nanofibrillar structures after the solvent annealing treatment. Besides this, both the deformability and optical properties of block copolymers were controllable by varying the PF/PBA ratio. The annealed PF4k-b-PBA7k thin film exhibited pure blue emission with a high photoluminescence quantum yield of over 22.5% under 100% strain, validating the excellent stretchability and promising stability. Furthermore, a stretchable and fluorescent PF-b-PBA based microporous template with tunable regularity can be fabricated through the breath figure method. These results demonstrated that the novel intrinsically deformable and luminescent rod-coil block copolymers could have versatile applications in stretchable light-emitting devices.

Influence of polymeric electrets on the performance of derived hybrid perovskite-based photo-memory devices

Organic-inorganic hybrid perovskite has become one of the most important photoactive materials owing to its intense light-harvesting property as well as its facile solution processability. Besides its photovoltaic applications, a novel photo-programmed transistor memory was recently developed based on the device architecture of a floating-gate transistor memory using a polymer/perovskite blend as the gate dielectric with the non-volatile memory characteristics of decent light response, applicable On/Off current ratio, and long retention time. In this study, we further clarify the influence of polymer matrix selection on the photo-response and memory properties of derived hybrid perovskite-based photo-memory devices. Four different host polymers, polystyrene (PS), poly(4-vinylphenol) (PVPh), poly(methyl methacrylate) (PMMA), and poly(methacrylic acid) (PMAA), were systematically investigated for comparison herein. This revealed that dissimilar chemical interactions existed between the host polymers and perovskite, resulting in the distinct memory behavior of the derived photo-memory devices, attributable to the different morphologies of the hybrid dielectric layers and the different sizes of the distributed perovskite nanoparticles (NPs). The photo-response behavior and the resultant On/Off current ratio increased as the size of the embedded perovskite NPs decreased, due to the enhanced photo-induced charge transfer across the dielectric/pentacene interface, benefiting from the better confinement effect of perovskite NPs in the polymer matrix. These results demonstrate the influence of perovskite NP aggregation at the dielectric/pentacene interface on the resultant memory behavior of the newly developed photo-memory device.